Anti-icing, de-icing, and heating configuration, integration, and power methods for aircraft, aerodynamic, and complex surfaces

ABSTRACT

Anti-icing methods and aerodynamic structures having laminated resistive heaters for de-icing are described. Several of the inventive aspects utilize laminated resistive heaters comprising a carbon nanotube layer and/or capacitors to store and supply electricity. The invention also includes methods of making aerodynamic structures having de-icing or anti-icing functionality.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/429,106 filed 31 Dec. 2010.

ABSTRACT

Anti-icing methods and aerodynamic structures having laminated resistiveheaters for de-icing are described. Several of the inventive aspectsutilize laminated resistive heaters comprising a carbon nanotube layerand/or capacitors to store and supply electricity. The invention alsoincludes methods of making aerodynamic structures having de-icing oranti-icing functionality.

INTRODUCTION

Forward facing aerodynamic surfaces, for example, wind turbines,propeller spinners, radomes, when exposed to atmospheric icingconditions are susceptible to ice build-up on the leading edge surface.If not removed, this accumulated ice can add excessive weight to thestructure and alter the airfoil configuration. For aircraft airfoils,this can cause undesirable and/or dangerous flying performance. Icebuild-up on the outside surface of a radome causes undesirableattenuation and distortion of the transmitted electromagnetic waves.

The patent literature describes numerous attempts for preventing orremoving ice from aerodynamic surfaces. For example, Petrenko et al. inU.S. Patent Application 2004/0149734 describe a system for iceprevention and removal with applications for airfoils etc. In one aspectan electrode grid system is described having a plurality of firstelectrode wires and second electrode wires separated by a grid spacingin a range of about 0.05 mm to 20 mm. The electrode wires coated with aninsulating layer that separates the wires electrically. A high-frequencyelectric field in accordance with the invention typically has a fieldstrength in a range of about from 100 V/cm to 100 kV/cm and a frequencynot less than 100 Hz. An alternating electric field is applied to theice to generate a resistive AC having a frequency greater than 1000 Hzin interfacial ice at interface. An AC power source provides a voltageof about 10 to 500 volts across the electrodes to create the alternatingelectric field. A portion of the capacitive AC associated with thealternating electric field is present in the interfacial ice asconductivity (resistive) AC, which causes dielectric loss heating.

Gafford et al. in U.S. Pat. No. 5,528,249 describe an anti-ice radomehaving a frequency selective surface and a plurality of resistiveheating elements. The frequency selective surface prevents the resistiveheating elements from disturbing the electromagnetic waves generated byan antenna within the radome, and therefore ice formation on the radomecan be prevented without sacrificing the transmission characteristics ofthe radome. Slotted conductive elements are formed using conventionalprinted circuit board fabrication techniques to achieve the necessaryprecision.

A major concern with traditional leading edge heating systems is theproblem when the melt water re-freezes as it flows backwards outside ofthe front heated panel. Typically after the ice melts along the leadingedge, the melt water flows aft of the heated surface where it freezes,resulting in what is commonly known as runback ice. Rutherford et al. inU.S. Pat. No. 6,330,986 describe an electrothermal zoned de-icing systemfor an aircraft employing a heat-conducting tape bonded to the leadingedge of an aircraft structure. The heat-conducting tape has a spanwiseparting strip area, and first and second ice accumulation and sheddingzones. The tape comprises a non-metallic electrical and heat conductinglayer consisting of a flexible expanded graphite foil laminated to anouter heat-conducting layer, in which the thickness of the flexibleexpanded graphite foil layer in the parting strip area is always greaterthan the thickness of the foil layer in either of the ice accumulationand shedding zones. The parting strip area thus has a decreasedelectrical resistance, a greater flow of current, and becomes hotterthan the zones in which the foil layer is thinner. Because the flexibleexpanded graphite foil is a monolithic structure that may be shaped,sculptured or layered to form different thicknesses in different areas,only a single control mechanism for a single set of electric terminalsis necessary to produce desired temperatures in the parting strip andice accumulation and shedding zones. When a predetermined amount ofelectric current is transmitted continuously through the tape, the outersurface of the heat-conducting outer layer at the parting strip isheated continuously to a temperature above 32° F. to maintain acontinuous ice-free (running wet) condition. At intermittent intervals,an increased electric current is applied to the tape to raise thetemperature of the outer surface of the heat-conducting outer layer atthe spanwise ice accumulation and shedding zones above 32° F. to melt orloosen accumulated runback ice. The runback ice is then aerodynamicallyremoved from the structural member by the airstream passing over theaircraft or by centrifugal forces when the aircraft structure is apropeller or rotor blade.

Resistive heating systems that can be applied to surfaces are known. Forexample, Shah et al. in WIPO Patent Application WO/2010/129234 describea resistive heating system constructed from to a composite structurethat includes a matrix material and a carbon nanotube (CNT)-infusedfiber material including a plurality of carbon nanotubes (CNTs) infusedto a fiber material. The CNT-infused fiber material is disposedthroughout a portion of the matrix material and the composite structureis adapted for application of a current through the CNT-infused fibermaterial to provide resistive heating of the matrix material to heat thecomposite structure.

Laminated resistive heaters are commercially available. For example,Thermo Heating Elements manufacture a Polymer Thick Film (PTF) heaterusing a polyester substrate in sheet or roll form. A polymeric,silver-based paste is first screen printed onto the polyester in thedesired circuit pattern, and this sheet or roll is then oven dried tocure or “set” the element. The circuits are then die cut apart, andterminals are added for lead attachment. The open face circuit is thencovered with a double-sided pressure sensitive adhesive (PSA) tape on apolyester substrate. One side of the PSA joins the top and bottom layersof the heater, while the other side of the PSA is used to apply theheater to the desired part to be heated. Eeonyx Corporation manufacturesEeonTex™ resistive heating fabric. It may be used in warming blankets;all-weather boots; and in use for de-icing of aircraft wings at highaltitude. A thermal electric heating product for anti-icing and de-icingthe leading edges of aviation vehicles is known as Thermawing™. Thissystems comprises a graphite film which is adhesively bonded onto thesurface of the wings. The installation is performed by the heatermanufacturer in their facility.

The patent literature provides additional examples of resistive heatersin laminated devices. To cite one example, Lawson et al. in U.S. Pat.No. 5,925,275 describe an electrically conductive composite heatingassembly. This invention relates to heater elements intended for use inapplications requiring high reliability in harsh environments. Thepatent reports that such heaters may be suitable for ice protectionsystems on aerospace structures, windmill blades or other likestructures

Various combinations of laminated resistive heaters with a pressuresensitive adhesive are described in the patent literature. For example,Keite-telgenbuescher et al. describe in US 2010/0213189 a resistiveheater comprising a pressure sensitive adhesive layer where theresistive heating layer comprises a polymer layer that may containcarbon nanotubes as a filler. The polymer layer comprises more than 50weight % polymer. Suggested applications for the laminated resistiveheater include wing deicing and wall heaters.

Bessette et al. in US 2005/0062024 describe imparting conductivity usingcarbon nanotubes to pressure sensitive adhesive for various applicationsincluding aerospace. The inventors describe a process for manufacturingcommercial quantities of tape by compounding in a conventional mixingapparatus an admixture of a PSA composition, carbon nanotubes, anyadditional fillers and/or additives, and a solvent or diluent. Theformulation may be coated or otherwise applied to a side of a backinglayer in a conventional manner. After coating, the resultant film may bedried to remove the solvent or otherwise cured or cooled to develop anadherent film on the backing layer. As a result of the inherent tack ofthe PSA film, an adhesive and/or mechanical bond may be developedbetween layers to form the integral, laminate tape. Alternatively, theadhesive layer may be separately formed and laminated under conditionsof elevated temperature and/or pressure to the backing layer in aseparate operation.

Feng et al. in US 2009/0314765 A1 describe a heater element comprising asubstantially polymer-free carbon nanotube coating on a substrate. Inone embodiment, a heater includes a planar support, heat-reflectinglayer, a heating element, a first electrode, a second electrode, and aprotecting layer.

Despite these efforts and other work, there remains a need for newsystems having better ice removal performance, longer life and decreasedweight and energy requirements.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a method for an anti-icing,de-icing, and/or a heating system for aircraft wings and forward facingaerodynamic surfaces, comprising a first heated section near the centralstagnation zone of the aerodynamic surface, and at least one upper andone lower heater section in areas aft of the central heater, whereinpower supplied to the central heated section is continuously applied,and wherein power supplied to the at least one upper and one lowerheater section is intermittently applied from charge stored in acapacitor. In preferred embodiments, the heater sectons compriseCNT-containing resistive heaters. Preferably, the temperature of thefirst heated section is permanently maintained above 32° F. (0° C.). Inthe preferred mode of operation, the heating of the first heated sectionprevents cupped or shelled icing from forming there. In some methods,the at least one upper and lower heater section in areas aft of thecentral heater shed runback icing after the formation of an ice sheet.

As with all the methods described herein, the invention also includes anairfoil comprising the components corresponding to the above method.

In another aspect, the invention provides a method of storing charge inan airfoil, comprising: providing a capacitor comprising a CNT resistiveheater layer, a layer comprising a carbon composite or metal surface,and a dielectric layer disposed between the CNT resistive layer and thecarbon composite or metal surface; wherein the carbon composite or metalsurface forms a structural component of the airfoil; and applying apotential between the CNT resistive layer and the carbon composite ormetal surface. In some preferred embodiments, the carbon composite ormetal surface comprises a wing, preferably wing made of a compositematerial; preferably a carbon composite. The invention also provides acorresponding device comprising the above-described components arrangedas described herein. In some preferred embodiments, charge from thecapacitor is used to power a CNT resistive heater layer to heat aportion of the exterior of the airfoil to remove ice or prevent iceformation.

The inventive aspects that employ a capacitor to power a resistiveheater can provide significant advantages in terms of energy efficiency(for example, utilizing excess energy) and reduced weight since it canreduce the need for batteries.

In a further aspect, the invention provides a method making an airfoilcomprising insulated electrical leads for powering a CNT heater systemwherein, channels are machined or molded into the airfoil surface, andpre-formed electrical insulators are installed into these channels, andelectrical power leads are installed into the insulators and contactingthe electric leads to a CNT heater layer. Preferably, the pre-formedelectrical insulators are made from a flexible plastic such aspolyethylene. In another preferred embodiment, the channel allows forthe electrical leads to remain flush with the outer wing surface wheninstalled so as not to disrupt the aerodynamic properties of the airfoilshape. Preferably, the pre-formed electrical insulator completelyencases the electrical lead where it passes through the hole in theairfoil (typically an aircraft wing). Also, preferably, the pre-formedelectrical insulator is open on top of the channel area allowing for theelectrical leads to contact with the CNT heater layer along its length;in preferred embodiments, the electrical insulator is open for acontinuous length of at least 3 cm (in some embodiments at least 10 cm),and the electrical lead is in direct contact with the CNT heater layerfor the length of at least 3 cm. In some preferred embodiments, theelectrical lead comprises a porous metal such as copper mesh or braidedcopper wires for superior contact with the CNT layer.

As mentioned before, the invention includes an airfoil comprising thefeatures described herein. For example, an airfoil having a channel inthe surface of the airfoil wherein the surface of the channel is coatedwith an electrical insulator and wherein an electrical lead is in thechannel; wherein the electrical insulator electrically insulates theairfoil from the electrical lead; wherein the electrical insulator doesnot completely surround the electrical lead over the length of thechannel on a surface of the airfoil; and wherein a CNT-containingresistive heating layer directly contacts the electrical lead in thechannel.

The invention further provides a targeted resistive heater, comprising:a plurality of vertically oriented electrode terminals in electricalcontact with a layer of conductive substrate, and a plurality ofhorizontally oriented electrode terminals in electrical contact with theconductive substrate forming an array of intersecting wires, wherein anelectrical switching network allows selected areas of the array to beselectively heated. The invention includes a method of using thistargeted resistive heater, comprising applying voltages at differentterminals such that the location of the heating is localized.

In another aspect, the invention provides a method for powering a CNTheater layer by induction. In this method, inductive coils arepositioned opposite each other on the inner and outer surfaces of anairfoil skin, at least one inductive coil is in electrical contact withthe CNT heater layer on the outer surface of the airfoil skin, andwherein the other inductive coil is on the inner surface of the airfoilskin and is in electrical contact with an AC power supply, and whereinAC current is applied to the inner coil which generates a current in theouter coil that powers the CNT heater layer. Preferably, the inductivecoil is in electrical contact with the CNT heater layer on the outersurface of the airfoil skin is a flattened coil protected with a plasticfilm; an example is an inductive coil printed onto a thin film. In someembodiments, the inductive coils are applied to the inner and outersurfaces of the wing by an adhesive. In a preferred embodiment, theairfoil is a wing and the inner coil is on the inside of the wing.

The invention also includes an airfoil having a CNT heater layer on theouter surface of the skin of the airfoil, comprising the components asin the above-described method. An advantage and feature of this aspectis that the airfoil skin can remain intact, there is no need to makeopenings in the airfoil skin for electrical connections to the resistiveheating layer.

The invention also provides a method of using a CNT layer as both aresistive heater and as an antenna, wherein an antenna comprising orconsisting of a CNT layer uses RF energy or additional electrical energyfor heating. In some preferred embodiments, the heating is used to deicethe surface of an airfoil.

The invention further provides a resistively loaded antenna having avarying resistance at differing points in the antenna. The antennacomprises a CNT layer having varying resistance at differing points inthe antenna. The varying resistance can be obtained by changingthickness of the CNT layer as a function of location, or changingresistance such as by varying dopant concentration as a function oflocation. This allows tailored control of RF propagationcharacteristics. The antenna may be planar—with a flat layer on a flatsubstrate. Alternatively, a CNT layer could coat three dimensionalantenna elements. As with all of the concepts described herein, theinvention also includes the corresponding method of making the structureand methods of operating the antenna. The antenna can be a patch antennafeedline or patch antenna array. The patch antenna can be of anygeometry including rectangular, circular, triangular, irregular, fractalor otherwise. The properties such as CNT layer thickness, resistance,and/or dopant concentration preferably varies by at least 5% (morepreferably at least 10%, in some embodiments at least 20%) over the areaor the length (either from one side to another or at any desired pointsalong the length).

For each of the inventive aspects, it is important to understand thatthe invention includes the method (such as the method of deicing, orheating or storing charge, or sending or receiving RF), the method ofmaking an article (such as making the wiring, making a flying vehiclethat includes the inventive structure), the inventive structures, andarticles of manufacture that include the inventive structure (such as anaircraft or component such as wing, nosecone, radome (for aircraft orstationary), or propeller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a cross-section of an aircraft wing with acentral heater 122 at the stagnation zone, and upper and lower heaters.

FIG. 2 schematically illustrates a heater circuit diagram incorporatingterminals, a capacitor, switches, and resistive heating elements.

FIG. 3 schematically illustrates blunt shaped aerodynamic surfaces.

FIG. 4 schematically illustrates a capacitor that include a section of awing.

FIG. 5 schematically illustrates a missile nosecone with central heaterand radial heating lines.

FIG. 6 schematically illustrates a surface 600 with 2, 3, or 4 radialheating lines 614 and a central heater 612.

FIG. 7 schematically illustrates a surface with the curved heating linesextending from a central heating region

FIG. 8 schematically illustrates an airplane nosecone with 3 radialheating lines and 3 heating panels.

FIG. 9 schematically illustrates a state of the art resistive heatingconfiguration.

FIG. 10 schematically illustrates a targeted heating grid schematic withvertical electrode terminals intersecting horizontal electrodeterminals.

FIG. 11 schematically illustrates a grid type electrode array.

FIG. 12 schematically illustrates a voltage/time distribution chart toillustrate selectively applying potentials as a function of time.

FIG. 13 schematically illustrates a temperature distribution profile ona patch antenna.

FIG. 14 schematically illustrates a configuration that allows a CNTlayer to function as both a resistive heater and as an antenna.

FIG. 15 schematically illustrates an inductively-powered CNT electricalcircuit 1540 situated adjacent an outer wing surface 1510.

FIGS. 16-19 illustrate airfoils having insulated electrical leadsintegrated into the surface of the airfoil.

FIG. 20 shows a flat conductive coil encased in a polymer and electricalleads attached to the coil.

FIG. 21 schematically illustrates a dipole that can be created with avarying resistance.

FIG. 22 schematically illustrates a microstrip patch antenna withincreasing resistance toward the edges.

GLOSSARY OF TERMS

An “aerodynamic surface” refers to a surface of an aircraft (such as anairplane or missile) over which a fluid flows. Most typically, anaerodynamic surface is a surface of a wing, blade, or nosecone.

An “airfoil” is a wing, fin, or blade. A wing skin typically has athickness between 0.01 cm and 2 cm. Some preferred airfoil skinscomprise carbon fiber and/or fiberglass composite materials.

The term “carbon nanotube” or “CNT” includes single, double andmultiwall carbon nanotubes and, unless further specified, also includesbundles and other morphologies. The invention is not limited to specifictypes of CNTs. The CNTs can be any combination of these materials, forexample, a CNT composition may include a mixture of single and multiwallCNTs, or it may consist essentially of DWNT and/or MWNT, or it mayconsist essentially of SWNT, etc. CNTs have an aspect ratio (length todiameter) of at least 50, preferably at least 100, and typically morethan 1000. In some embodiments, a CNT network layer is continuous over asubstrate; in some other embodiments, it is formed of rows of CNTnetworks separated by rows of polymer (such as CNTs deposited in agrooved polymer substrate).

“Dielectric” is a well known term that refers to an electricallyinsulating material that can be polarized in an electric field. Commondielectrics are ceramics and plastics.

A “patch antenna” is an antenna comprising a sheet of conductivematerial that has a thickness that is much smaller than both width andheight; typically at least ten times smaller than either width orheight. For purposes of the present invention, the conductive sheetcomprises CNTs.

A “stagnation” zone is a volume where flow is relatively stagnant. Thisoccurs most typically at the leading edge of a wing where ice can buildup.

A “structural component” of an airfoil means a component that supportsthe structure of the airfoil; it is not a component exclusively used ina capacitor but it also supports the mechanical integrity of theairfoil. A typical example is the metal, or more preferably, carboncomposite, that makes up a surface of a wing.

The invention is often characterized by the term “comprising” whichmeans “including.” In narrower aspects, the term “comprising” may bereplaced by the more restrictive terms “consisting essentially of” or“consisting of.”

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the invention provides a method for anti-icing, de-icing,and a heating system for aircraft wings and forward facing aerodynamicsurfaces, for example, wind turbines, propeller spinners, aircraftradomes, and nosecones. The invention comprises a first heated sectionnear the central stagnation zone to prevent cupped or shelled icing fromforming there, and at least one upper and lower heater section in areasaft of the central heater. Typically, runoff melt-water from the centralheater will refreeze together with other ice accumulation. Byperiodically activating the upper and lower heaters to melt or break-upthe ice-to-surface interface, the accumulated ice will be removed byaerodynamic (or other) forces.

FIG. 1 shows a schematic 100 of a cross-section of an aircraft wing 112,central heater 122 at the stagnation zone, lower heaters 114 and 116,upper heaters 118 and 120, ice layer 126, and aerodynamic streamlines124. As an alternative arrangement, FIG. 3 schematically illustratesapplications 300 to blunt shaped aerodynamic surfaces such as propellerspinners 314, aircraft radomes 318, 320, 322, or nosecones 312, 316(which may be radomes). For example, FIG. 5 illustrates a missilenosecone 500 with central heater 512 and radial heating lines 514, thuscreating heating sections B, C, and D aft of the central heater 512.FIG. 6 illustrates a surface 600 with 2, 3, or 4 radial heating lines614 and a central heater 612. FIG. 7 illustrates a surface 700 where theradial heating lines 712 extending from central heating region 714 maybe curved. Intersecting heating lines 716 allow for complex heatingzones to be formed. FIG. 8 illustrates an airplane nosecone 800 with 3radial heating lines and 3 heating panels B, C and D. The accumulatedice 812 is removed after triggering heating zones B, C and D.

A potential icing shell can be prevented from forming by heating radialzones outward from a region near the aerodynamic stagnation point. Atleast two radial heating lines would be needed but possibly three ormore would function better. These would provide radial heating lines tobreak up icing shells into pieces that can be shed aerodynamicallyand/or due to centrifugal forces.

In operation, central heaters along the stagnation line or zone would begenerally heated continuously, but alternatively may be heatedintermittently. The heating areas aft of the stagnation line or zone,would generally be heated intermittently, but also could be heatedcontinuously if desired. With this heating arrangement, the inventionprovides significant power consumption reduction (electrical in the caseof electrothermal heaters, but could be engine power in case of enginebleed air), since all the supercooled impinging cloud droplets are notcontinuously heated—only those at the very leading edge near thestagnation zone.

Since the use of resistive heating panels with varying thicknesses canaffect aerodynamics, in some preferred embodiments, the heating panelsare equally thick; differential heating can be obtained by selectivelyheating each panel. In some embodiments, one or more ice sensors areused to monitor ice formation—thus, heating can be applied locally (tothe desired panel(s)) and in the appropriate amount in response to iceformation or ice formation conditions. The central panel can beseparated from the other panels by significant distances—for example thecentral panel and the upper panel can be separated by at least 1 cm, orat least 2 cm. Intermittently heating the upper panel enables removingice in chunks, so that any ice in the gap between panels would beremoved. Typically, any gap between panels would be filled by aninsulating material—preferably the same polymer that overlies the CNTs.

The resistive heaters (which may also be referred to as heating panelsor resistive heating coatings (RHC) may be conventionally powered; morepreferably, especially for intermittent heating, power is supplied tothe resistive heaters from electrically connected capacitors. Theintermittent heating could be powered by capacitors, and FIG. 2 shows aschematic 200 for a heater circuit diagram incorporating terminals 212,a capacitor 224, switches 226, 228, and resistive elements 214, 216,218, and 220. The capacitor can include a CNT resistive heater.

Supercapacitors or ultracapacitors can be used as an electrical powersource for the resistive heating elements in place of batteries.Compared to batteries, such capacitors are better for repeated cyclingand quick charging/discharging and, if required, providing shortduration high current pulses. The number and quantity of such capacitorsdepends on the overall design of the power system and the requiredoperational duty of the resistive heaters in icing conditions. Forexample, if the onboard aircraft power for the anti icing system issmall then the more capacitors that are used, the more energy that canbe stored and subsequently delivered to the heating elements to increasetemperature or duration. In some preferred embodiments, there are atleast two such capacitors on each wing or aerodynamic surface; in someembodiments, at least 3; and in some embodiments, at least 6 suchcapacitors on each wing or aerodynamic surface.

Supercapacitors or ultracapacitors work very well in conjunction withthe system that requires intermittent power to upper and lower resistiveheaters. The capacitors can be powered (relatively slowly) from excessengine power, and then discharged (relatively quickly) to provide apulse of power to a resistive heating panel. The invention can solvemultiple problems. First it reduces the power requirement and/or needfor batteries. Second it increases the available power density for thecenter heater. Third it can prevent runback icing, since the ice willcollect in the areas over the upper and lower heaters because thestagnation heating area is small. Fourth, it can facilitate lower powerusage by shedding ice in chunks, rather than trying to continuously keepall the impinging supercooled cloud droplets in liquid form (orevaporate them). It is a much smarter use of available power.

The invention provides a method that allows a CNT resistive heater tofunction as a capacitor due to the base dielectric gap to a substrate,comprising the CNT layer on top of a dielectric layer, on top of acarbon composite (or, less preferably, metallic) wing. Upper and lowerintermittent heating zones are well suited to a cyclical capacitor powerstorage scheme. Lightweight and high power density super or ultracapacitors can be used to accumulate charge, which can then be pulsed toget a rapid heating of the upper and lower zones thereby shedding theaccumulated ice from the impinged cloud droplets and the refrozen runofffrom the center heater. The upper and lower heaters can be triggeredfrom ultra or super capacitors due to their intermittent operation. Inthis fashion, the system can be applied to aircraft with low peak poweravailability.

The combination of the CNT layer and the conductive wing separated by anelectrical insulating layer comprises the major elements of a capacitor.Therefore, the system layout allows it to also be used as a capacitor;in some embodiments using one charged resistive heating panel to poweranother panel for de-icing. FIG. 4 shows a schematic illustration 400 ofthe major components of this system. A wing section 408 forms one plateof the capacitor. A dielectric layer 406 separates the wing section froma CNT resistive heating element 404 that forms the second plate of thecapacitor. A protective film 402, which is typically a polymer coating,protects the CNT layer.

In some embodiments, electrical leads are used to power the resistive(preferably CNT-based) heater system. If these leads need to be passedthrough or be in contact with a conductive layer such as a carbon fiberwing skin, then the electrical leads must be thoroughly electricallyinsulated from the wing substrate. This insulation can be achieved byapplying a primer coating, but coating thickness and uniformity can bedifficult to control in order to ensure no pin-holes exist causing anelectrical short. FIGS. 16-19 illustrate airfoils having insulatedelectrical leads integrated into the surface of the airfoil. FIG. 16shows a schematic 1600 of a cross-section of an airplane wing, with twochannels 1650 sunken into the wing 1670. Pre-formed electricalinsulators 1630 are installed into the channels, and electrical powerleads 1610 and 1620 are then installed into the insulators andelectrical contact made with the CNT heater layer 1640. FIG. 17schematically illustrates a different angle 1700 of FIG. 16. In FIG. 17the electrical lead 1710, completely encased in insulator 1730, passesthrough a via 1780 in the wing 1790 and continues through channel 1750at the outer surface of the wing. When the electrical lead reaches theCNT layer 1740, the pre-formed insulator only partially encases theelectrical lead such that the electrical lead can make electricalcontact with the CNT layer 1740. FIG. 18 presents another view 1800 ofthe same construction in which an electrical lead 1810, completelyencased in insulator 1830, passes through a via in the wing 1890 andcontinues through channel 1850 at the outer surface of the wing. Thecutaway view 1900 in FIG. 19 illustrates the connection of electricallead 1910 to CNT layer 1940. The electrical lead is insulated from thewing by insulation 1930. An important aspect of this inventive conceptis that the channels allow for the electrical leads to remain flush withthe outer wing surface when installed so as not to disrupt theaerodynamic properties of the shape, see FIG. 19. The pre-formedinsulator could be made from any electrically insulating material, butpreferably from a flexible plastic such as polyethylene. The electricallead is preferably completely encased as it passes from the interior ofthe airfoil through the skin 1860 to the exterior of the airfoil, thenon the exterior of the airfoil the electrical lead preferably is open(on the exterior side only) along a length of the channel in order tocontact the resistive heating layer; preferably the contact is for alength of at least 3 cm, in some embodiments at least 5 cm.

The wiring is preferably a porous or surface-roughened conductivematerial—this will provide superior contact to a CNT resistive heatingsheet. Preferred types of wiring include copper mesh and flattenedcopper braids. It is believed that these conductors allow for capillaryaction to draw the CNT-fluid into intimate contact with the conductorimproving the bond between carbon nanotubes and the electrode;especially with the CNT layer is formed from a coating mixture depositedonto the surface 1870 comprising the exposed electric lead 1710.

In yet another aspect, the invention provides a method for targetedheating areas of nearly unlimited shapes, comprising a grid type lead orelectrode array wherein an electrical switching network allows differentareas to be arbitrarily heated up at will by cycling power through thedesired leads. FIG. 9 shows schematic 900 of a state of the artresistive heating layout with electrodes 914, and conductive layer 912.FIG. 10 illustrates a targeted heating grid schematic 1000, withvertical electrode terminals 1020 intersecting the horizontal electrodeterminals 1040 and their associated power leads forming the array, notlabeled. Either applied on top of, or sandwiched between the powerlines, lies the resistive heater (preferably a CNT layer). A gap 1060exists between the power lines allowing the vertical terminals 1020 andhorizontal terminals 1040 to be powered independently without shorting.By having a grid of electrodes and applying voltages at differentterminals, the location of the heating can be localized. Further bymodulating the phase and or timing between different terminals, almostany heat distribution pattern can be generated on the array. FIG. 11shows such a simple schematic 1100, with microcontroller 1120, switchingnetwork 1130, power supply 1140 and grid type lead or electrode array1110. FIG. 12 illustrates schematic 1200 of a voltage/time distributionchart to illustrate selectively applying potentials as a function oftime, and FIG. 13 illustrates schematic 1300 of an associatedtemperature distribution profile.

The grid pattern for the RHC system differs from LCD-TFT (or similar)based grids in that this concept focuses on controlling localizedheating in a desired area. This allows for the application of the RHCsystem in bulk across an area, while only applying heat energy in thedesired areas of the grid as needed.

In another aspect the invention provides a method for powering the CNTheater layer through inductive means, and hence avoiding the need todrill holes through the airplane wing for example. The inventioncomprises attaching inductive coils to the inner and outer surfaces ofthe wing, wherein one of the inductive coils is in electrical contactwith the CNT heater layer, and wherein the other inductive coil is inelectrical contact with an AC power supply. In FIG. 15, schematic 1500illustrates the inventive concept. AC power supply 1550 and electricalcoil is situated adjacent the inner wing surface 1520, and theinductively-powered CNT electrical circuit 1540 is situated adjacent theouter wing surface 1510, thereby heating CNT layer 1530. The inductivecoils may be printed onto thin films for example 3M aero laminate, andthen applied to the inner and outer surfaces of the wing by an adhesive.AC power is required instead of DC power for this induction heatingconcept, but not to the detriment of the thermal performance of the CNTheater layer. Preferred coils comprise flattened coils in a layer ofmaterial such as a polymer. See FIG. 20 which shows the flat coilencased in a polymer and electrical leads that can be used to connect toa resistive heating element. In a preferred embodiment, one coil isinside a wing while a second coil is adjacent a heating panel on or nearthe outer surface (i.e., adjacent or near the atmosphere). Preferably,the coils are directly opposite each other. When powering the insidecoil with AC power, an electromagnetic field is produced. Thiselectromagnetic field then creates a current in the outer surface coilthrough induction even though the coils are separated by a gap.Together, this pair of coils create a transformer. The current from theouter coil is used to power a resistive heating element. The inner coilcan be either flat or cylindrical; the outer coil is preferably flat tominimize any effects on the aerodynamic properties of the airfoil. Theresulting structure may have fewer defects since the resistive heatingelement can be powered without drilling holes through the wing. Thecoils are preferably protected with a polymer coating and can beattached to the airfoil by an adhesive or other suitable means.

In another aspect the invention provides a method that allows the CNTlayer to function as both a resistive heater and as an antenna. In FIG.14, when DC power is applied between electrode connections A&C andbetween electrode connections B&D an area of the resistive heater (e.g.,the CNT layer) is heated. If, in FIG. 14, Radio Frequency (RF) isapplied between electrode connections A&B an antenna affect is observed.The electromagnetic radiation may be controlled by fine tuning thematerial resistance of the CNT layer. Resistance in the antenna RFelements may be undesired, however one interesting effect is that theresistance changes with temperature, so heating the elements may allowsome useful effect of active resistance control. Alternatively, the onlyelectrical connection point for the dipole drawn in FIG. 14 may bepoints A&B where RF power is introduced. The resistive power dissipationof the CNT layer can transform some of the RF energy directly into theheating of the dipole elements.

Most antennas have high conductivity throughout their elements andcontrol the radiation with their structure (dipoles, yagis,log-periodic, helicals, etc.). Although this can also be done with theproper shaping of the CNT area, the electromagnetic radiation can becontrolled by fine tuning the material resistance of the CNT layerthrough composition, thickness, or geometry. High resistance in theantenna RF elements may be undesired, but some resistance is desired forthermal heating performance.

Also, the CNT technology is ideally suited for creating resistivelyloaded antennas of various shapes because it can be printed, sprayed,etched or painted on substrates to obtain various shapes. Importantlythe local resistance can be varied throughout the shape. Thus, a dipolecan be created with a varying resistance from the drive point (feed linepoint where RF is introduced) to the outer tips of the dipole elements.FIG. 21 shows a schematic 2300 of the inventive concept as applied to adipole. A CNT dipole from 2330 to 2340 can be deposited on a suitableinert substrate 2350. The CNT resistance can increase outward from 2330to 2340 as indicated by progressively darker shading. An RF source 2310provides energy through feedlines 2320 to the antenna drive point 2330.Only one such resistance variation of many possibilities is shown.Various distributions can be conceived to tune antenna propagation andimpedance characteristics. Additionally the concept can be applied topatterned loop, bowtie, and multi-element shapes. Also the CNT layer canbe used in a three dimensional way. For example, a dipole or yagielement can be made from some suitable inert rods and coated with a CNTlayer at its surface to create a resistively loaded three dimensionalstructure.

Another example is that the system can easily be used as a resistivelyloaded patch antenna due to its customizable geometry, i.e. a groundplane surface (airplane outer wing skin), dielectric layer(primer/laminate), and conductor (CNT layer). Again, this could allowthe system to be heated while also using it as an antenna, butimportantly, the ability to tailor the resistive loading throughout theelement(s) can allow for tunable antenna properties which fixedresistance elements do not provide. FIG. 22 shows a schematic 2400 ofthe inventive concept as applied to a microstrip patch antenna 2460. Therectangular patch antenna is fed at the drive point 2450 via feedlines2440 from the RF source 2410. A dielectric 2430 separates the patchelement from the ground plane on the bottom 2420. Preferably, there is avarying resistance in the patch element 2460. The patch antenna is shownwith shading from the center outwards to represent one possibledistribution of CNT resistance with increasing resistance toward theedges. Other CNT resistance distributions are plausible (for example,increasing from one side to the other over any desired length orincreasing over the entire length of the patch element in any direction)and can be used for tuning the antenna propagation characteristics (i.e.radiated field strength as a function of direction) for specificapplications. Also the geometric shape need not be constrained torectangular arrays, and this resistively loaded invention can be appliedto all the other antenna patch shapes: such as circles, triangles,fractals, and other geometries.

Throughout this disclosure is mentioned a resistive heating layer orcomponent, sometimes referred to as an RHC. In its broadest aspect, thiscan be any resistive heater; preferably, however, the resistive heatingcomponent is a Carbon Nanotube (CNT) based resistive heater which isbelieved to provide numerous advantages over other types of resistiveheaters. Examples of CNT resistive heaters are disclosed inWO2010/132858, which is assigned to Battelle Memorial Institute.

The term “carbon nanotube” or “CNT” includes single, double andmultiwall carbon nanotubes and, unless further specified, also includesbundles and other morphologies. The invention is not limited to specifictypes of CNTs. The CNTs can be any combination of these materials, forexample, a CNT composition may include a mixture of single and multiwallCNTs, or it may consist essentially of DWNT and/or MWNT, or it mayconsist essentially of SWNT, etc. CNTs have an aspect ratio (length todiameter) of at least 50, preferably at least 100, and typically morethan 1000.

A CNT network can be prepared, for example, as a dispersion of CNTsapplied directly to a substrate where the solvents used in thedispersion process are evaporated off leaving a layer of CNTs thatcoagulate together into a continuous network. The CNT network may beprepared from dispersions and applied by coating methods known in theart, such as, but not limited to, spraying (air assisted airless,airless or air), roll-coating, gravure printing, flexography, brushapplied and spin-coating. The thickness of the CNT layer is in the rangefrom 0.005 μm to 100 μm, preferably in the range of 0.05 μm to 100 μm,more preferably in the range of 0.3 μm to 100 μm.

The CNT layer may include other optional additives such as p-dopants.P-dopants could include, but are not limited to, perfluorosulfonicacids, thionyl chloride, organic pi-acids, nitrobenzene, organometallicLewis acids, organic Lewis acids, or Bronsted acids. Materials thatfunction as both dispersing agents and dopants such as Nafion andhyaluronic acid may be present. These materials contain p-dopingmoieties, i.e. electron accepting groups, within their structure, oftenas pendant groups on a backbone. Generally, these additives will bepresent as less than 70% by weight of the CNT film, and in someembodiments as less than 50% by weight of the CNT film. Polymers andcarbohydrates that function as both dispersing agents and dopants can bedistinguished from other polymer materials, i.e. those functioning asonly a dispersing agent or those functioning as a structural component.Because of the presence of electron accepting moieties, these materialscan form a charge transfer complex with semiconducting CNTs, whichp-dopes the semiconducting CNTs and raises the electrical conductivity.Thus, these dual dispersing agent/dopants can be tolerated at a highermass percentage within the CNT layer than other types of polymermaterials or surfactants.

The thickness of a coating composition over the CNT material ispreferably 2 mm or less, more preferably 150 μm or less, preferably 50μm or less, in some embodiments, a thickness of 250 nm to 50 μm; thickerlayers can experience foaming or bubbling during application that leadsto pathways for a subsequent topcoat to penetrate and disrupt theconductivity of the CNT layer.

A coating composition can be applied to the CNT network by knownmethods; for example, bar coating or spraying. Techniques, such astroweling, that disrupt the CNT network should be avoided. Afterapplication of a protective coating to the CNT network, the coatedsubstrate can be cured (in some embodiments, curing is conducted atambient temperature). In the curing operation, the film formingmaterials crosslink to leave a mechanically durable and chemicallyresistant film.

A multilayered laminate resistive heater could be manufactured withconventional roll coat equipment. The electronic leads could be printedon a base substrate, such as 3M's Aerospace quality protective film. Thecarbon nanotube dispersion can then be applied to the film printed withcircuitry with conventional roll coating methods. The protective coatingcould also be applied in this manner in-line.

In some embodiments, the CNT is substantially polymer-free such thatpolymer (if present) does not significantly affect the electricalproperties of the layer; preferably, the interior of the CNT layercontains 10 weight % polymer or less, more preferably 5 wt % or less,and still more preferably 2 wt % or less. In some embodiments, apressure sensitive adhesive (PSA) is present on the major side of thesubstrate opposite the side over which the CNT layer is disposed. ThePSA can be used to adhere the resistive heater to the outer surface ofan airfoil.

A resistive heater laminate can be applied in the field since thesubstrate can be backed with a pressure sensitive adhesive (an adhesivethat bonds to a substrate by the application of pressure) and a releaselayer. The release layer would be removed and the laminated heaterapplied to a substrate like a sticker. A more permanent installation ofa laminate heater can be applied with a structural adhesive such asepoxy instead of a pressure sensitive adhesive.

The aqueous or non-aqueous solvent present in common aerospace topcoats, when applied to a CNT material, may disrupt the electricalproperties of the CNT material by several mechanisms. One mechanism isby increasing the electrical resistance between adjacent CNTs. Topcoatsdissolved in solvents can infiltrate the CNTs, permitting the topcoatresin system to permeate and cure between the individual CNT fibers. TheCNTs require intimate contact to transport electrical charge from oneCNT to another; charge transport takes place though either tunneling orhopping. If a non-conductive polymer resin remains between the CNTs, itprevents close contact of CNTs, which increases the energy associatedwith electron hopping or tunneling, and behaves as a high resistanceresistor in series. The effect is that the bulk conductivity of the CNTmaterial is reduced significantly. Treatment of CNTs with surfactants ordispersing agents is often used to improve their interaction with wateror solvents. After film formation; these surfactants and dispersingagents often remain in the film, continuing to modify the surfaceproperties of the CNTs. This renders the CNT layer more susceptible topenetration by aqueous or non-aqueous solvents. To avoid this problem,in some preferred embodiments, a solvent-free protective layer can beused to prevent the change in resistance that accompanies theapplication of either organic-solvent-based or water-based coatings toCNT materials. In some preferred embodiments, a polyurethane coating isin direct contact with the CNT layer.

In some preferred embodiments, the substrate is an airplane or part ofan airplane such as a wing. The geometric surface area (that is, thearea that can be measured by a ruler rather than BET surface area) ofthe coated article is preferably at least 0.5 cm×0.5 cm, more preferablyat least 1 cm×1 cm, in some embodiments at least 5 cm×5 cm.

The polymer protective coating provides sufficient chemical resistanceso as to prevent solvents (including water), or other environmentalhazards from subsequently applied coatings or solvents from penetratingthe polymer and disrupting the CNT network or changing its conductivitysignificantly.

Prior to coating with a polymer or polymer precursor composition (toform the protective coating), a CNT network layer is preferably in theform of a CNT/air composite, for example a CNT network film, a paper orcloth-like layer of CNTs, or a macroscopic fiber of CNTs. CNT networklayers of the present invention preferably contain at least 25 weight %CNT, in some embodiments at least 50 wt %, and in some embodiments 25 to100 wt % CNT. The CNTs can be distinguished from other carbonaceousimpurities using methods known to those skilled in the art, includingNIR spectroscopy (“Purity Evaluation of As-Prepared Single-Walled CarbonNanotube Soot by Use of Solution-Phase Near-IR Spectroscopy,” M. E.Itkis, D. E. Perea, S. Niyogi, S. M. Rickard, M. A. Hamon, H. Hu, B.Zhao, and R. C. Haddon, Nano Lett. 2003, 3(3), 309) Raman,thermogravimetric analysis, or electron microscopy (Measurement Issuesin Single Wall Carbon Nanotubes. NIST Special Publication 960-19). TheCNT network layer (again, prior to coating) preferably has little or nopolymer (“polymer” does not include CNTs or carbonaceous materials thattypically accompany CNTs—typical examples of polymers includepolyurethane, polycarbonate, polyethylene, etc.); preferably the networklayer comprises less than 5 wt % polymer, more preferably less than 1 wt%) The volume fraction in the network layer is preferably at least 2%CNTs, more preferably at least 5%, and in some embodiments 2 to about90%. The remainder of the composite may comprise air (by volume) and/orother materials such as residual surfactant, carbonaceous materials, ordispersing agent (by weight and/or volume). “Substantially withoutpolymer” means 5 weight % or less of polymer in the interior of a CNTfilm, preferably the film has 2 weight % or less of polymer, and stillmore preferably 1 weight % or less of polymer in the interior of the CNTfilm. This is quite different from composite materials in which CNTs aredispersed in a polymer matrix.

After the CNT network layer has been coated, it retains electricalconductivity provided by contacts between CNTs; it is preferably not adispersion of CNTs in a polymer matrix. Typically, a cross-sectionalview of the composite material will show a polymer layer that containslittle or preferably no CNTs and a CNT network layer that comprises CNTs(and possibly other carbonaceous materials that commonly accompany CNTs,as well as surfactants) with little or no polymer. Preferably, a CNTnetwork layer that has an overlying polymer coating comprises 50 mass %or less of the coating polymer within the CNT layer, more preferably 25mass % or less, and still more preferably 10 mass % or less of thecoating polymer within the layer. Preferably, a CNT layer comprises atleast 25 mass % CNTs and carbonaceous materials, and preferably at least50 mass % CNTs and in some embodiments 30 to 100 mass % CNTs. CNTnetworks and CNT fibers have very distinct rope-like morphology asobserved by high resolution SEM or TEM. See for example Hu, L.; Hecht,D. S.; and Gruner, G. Nano Lett., 4 (12), 2513-2517 for CNT networks andU.S. Pat. No. 6,683,783 for images of CNT fibers. Because the CNT layerstypically contain little or no polymer, they exhibit surface roughness,if characterized by AFM, associated with the CNT diameter and bundlesize, in the range of 0.5 to 50 nm. Preferably, the coating compositioncontacts the surface of the CNT network layer but does not fill spaceswithin the network layer. Penetration of a coating into the CNT layercould also be determined by cross-section of the multi-layer sample andthen analysis by methods such as SEM-EDS or XPS; the CNT layer ispreferably substantially free from N-groups that are associated with thetopcoat.

CNT layers have many contacts between CNTs and good conductivity thatis, a resistivity less than 0.05 Ω·cm, preferably less than 0.002 Ω·cm.The sheet resistance of this layer should be less than 500 Ω/square,preferably less than 200 Ω/square, more preferably less than 50Ω/square. The CNT layer may be planar, cylindrical, or other contiguousgeometry; in some preferred embodiments, the CNT layer is substantiallyplanar (similar to a sheet of paper or a nonwoven textile sheet, a fewfibers may project from a planar layer). These are preferredcharacteristics of the CNT layer both before and after a coating isapplied over the CNT layer.

In some embodiments, solventless, preferably 100% solids, (free oforganic and water solvent) suitable isocyanate compound or mixture ofcompounds can be used as the curing agent to form the protective layer.To function as an effective crosslinking agent, the isocyanate shouldhave at least two reactive isocyanate groups. Suitable polyisocyanatecrosslinking agents may contain aliphatically, cycloaliphatically,araliphatically and/or aromatically bound isocyanate groups. Mixtures ofpolyisocyanates are also suitable. Polyisocyanate containingaliphatically, cycloaliphatically, araliphatically and/or aromaticallybound polyisocyanate groups are also suitable. This includes, forexample: hexamethylene trimethylhexamethylene diisocycante,meta-α,α,α′,α′-tetramethylxylylenediisocyanate,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane (isophoronoediisocyanate or “IPDI”), bis(4-isocyanatocyclohexyl)methane (hydrogenateMDI), toluene diisocyanate (“TDI”), hexamethylene diisocyanate (“HDI”)or biuret derivatives of various diisocyanates.

In addition to the components discussed above, other additives can alsobe incorporated such as cure catalysts. Cure catalysts for isocyanateare well known to those skilled in the art such as organometalliccatalysts and, particularly, organotin compounds such as dibutyltindiacetate, dibutyltin dioxide, bibutyltin dilaurate and the like. Otheroptional ingredients such as surfactants, defoamers, thixotropic agents,anti-gassing agents, flow control agents, pigments, fillers, and otheradditives without added organic or water solvents may be included in thecomposition. In preferred embodiments, the polymer precursor compositioncomprises at least 90 mass %, more preferably at least 95 mass % (insome embodiments at least 98 mass %) of components that, after curing,are bonded to the polymer structure.

The thickness of the coating composition over the CNT material ispreferably 2 mm or less, more preferably 150 μm or less, preferably 50μm or less, in some embodiments, a thickness of 250 nm to 50 μm.

A coating composition can be applied to the CNT network by knownmethods; for example, bar coating or spraying. Techniques, such astroweling, that disrupt the CNT network should be avoided; althoughtroweling might be used in the case where a grooved substrate protectsthe CNTs. After application of a protective coating to the CNT network,the coated substrate can be cured (in some embodiments, curing isconducted at ambient temperature). In the curing operation, the filmforming materials crosslink to leave a mechanically durable andchemically resistant film.

The sheet resistance of the CNT layer before coating may be determinedby standard 4-point probe methods or other known methods for determiningsheet resistance. The impact of the subsequent coatings on the sheetresistance of the underlying material may be determined by one ofseveral methods, depending on the applications of interest. Metallicleads, such as silver painted leads, may be applied under or over theCNT layer and the resistance measured. Subsequent overcoats may then beapplied on top of the CNT layer and the resistance re-examined.Application of the coating of this invention should result in less than81% change in resistance, preferably less than 10% change in resistance,and still more preferably less than 5% change in resistance, aftercuring the coating. Likewise, application of subsequent layers on top ofthis stack should not increase the resistance by more than 5%,preferably by 3% or less. Alternatively, one could measure the shieldingeffectiveness of a CNT film before and after application of coatings,using a method such as SAE ARP-1705. Application of the coating of thisinvention should result in less than 38% change in shieldingeffectiveness, more preferably less than 5% after curing the coating.Likewise, application of subsequent layers on top of this stack (thatis, the CNT network layer and the protective coating) should notdecrease the shielding effectiveness by more than 5%.

1. A method of storing charge in an airfoil, comprising: providing acapacitor comprising a CNT resistive heater layer, a layer comprising acarbon composite or metal surface, and a dielectric layer disposedbetween the CNT resistive layer and the carbon composite or metalsurface; wherein the carbon composite or metal surface forms astructural component of the airfoil; and applying a potential betweenthe CNT resistive layer and the carbon composite or metal surface. 2.The method of claim 1 wherein the carbon composite or metal surfacecomprises a wing.
 3. The method of claim 2 wherein the wing comprises acomposite material.
 4. The method of claim 3 wherein the compositematerial comprises a carbon composite.
 5. An airfoil comprising acapacitor comprising a CNT resistive heater layer, a layer comprising acarbon composite or metal surface, and a dielectric layer disposedbetween the CNT resistive layer and the carbon composite or metalsurface; wherein the carbon composite or metal surface forms astructural component of the airfoil.
 6. A method of providing power tothe CNT resistive heater layer of claim 5 comprising: charging and thendischarging current from the carbon composite or metal surface. 7-9.(canceled) 10-15. (canceled)
 16. An airfoil, comprising: a channel inthe surface of the airfoil wherein the surface of the channel is coatedwith an electrical insulator and an electrical lead disposed in thechannel; wherein the electrical insulator electrically insulates theairfoil from the electrical lead; wherein the electrical insulator doesnot completely surround the electrical lead over the length of thechannel; and wherein a CNT-containing resistive heating layer contactsthe electrical lead in the channel.
 17. The airfoil of claim 16 whereinthe airfoil is a wing and wherein the electrical lead passes through avia in the skin of the wing and wherein the electrical lead iscompletely encased in the electrical insulator though the via thatpasses through the skin and connects to the channel. 18-20. (canceled)21. An airfoil having a CNT heater layer on the outer surface of theskin of the airfoil, comprising: inductive coils that are positionedopposite each other on the inner and outer surfaces of an airfoil skin,wherein one of the inductive coils is in electrical contact with the CNTheater layer on the outer surface of the airfoil skin, and wherein theother inductive coil is on the inner surface of the airfoil skin and isin electrical contact with an AC power supply. 22-25. (canceled)
 26. Theairfoil of claim 16 where the electrical insulator is made from aflexible plastic.
 27. The airfoil of claim 16 wherein the channel allowsfor the electrical leads to remain flush with the outer wing surfacewhen installed so as not to disrupt the aerodynamic properties of theairfoil.
 28. The airfoil of claim 16 wherein the electrical insulatorcompletely encases the electrical lead where it passes through the holein the wing.
 29. The airfoil of claim 16 where the electrical insulatoris open on top of the channel area allowing for the electrical leads tocontact with the CNT heater layer along a length of at least 3 cm. 30.The airfoil of claim 16 wherein the electrical lead is porous or has aroughened surface.
 31. The airfoil of claim 21 where the inductive coilsare printed onto thin films and applied to the inner and outer surfacesof the wing by an adhesive.